The concept of frameless stereotaxy is now emerging in the field of neurosurgery. What is meant by this is quantitative determination of anatomical positions on, let us say, the head based on data taken from a CT, MRI or other scanning needs. The data from the image scan can be put into a computer and the head represented, according to this graphic information. It is useful for the surgeon to know where he will be operating relative to this data field. He can, thus, plan his operation quantitatively based on the anatomy as visualized form the image data. Until now the use of stereotactic head frames for fixation means is commonplace. For example, see U.S. Pat. No. 4,608,977, issued Sep. 2, 1986, and entitled: System Using Computed Tomography As For Selective Body Treatment, Brown. These employ a head fixation device typically with an index means that can be visualized in scan slices or image data. Thus, the anatomical stereotactic data so determined can be quantified relative to the head frame. Arc systems or probe carriers are typically used to direct a probe quantitatively based on this data relative to the head holder and, thus, to the anatomy. If the surgeon can be freed from the use of the head holder and localizer, and still relate positions in the anatomy to things seen on the scan or image data, then this can spare patient discomfort and could be potentially used for general neurosurgery where only approximate target positioning is needed. For example, a space pointer which could be directed to the anatomy and its position could be quantified relative to the stereotactic image data. This space pointer, analogous to a pencil, might be therefore pointed at a position on the anatomy and the position and the direction of the pointer, subsequently appear, on the computer graphics display of the anatomical data. Such apparatus has been proposed, using an articulated space pointer with a mechanical linkage. In that regard, see an article entitled "An Articulated Neurosurgical Navigation System Using MRI and CT Images," IEEE Transactions on Biomedical Engineering, Volume 35, No. 2, February 1988 (Kosugi et al), incorporated by reference herein. It would be convenient if this space pointer were mechanically decoupled or minimally mechanically coupled. Until now, several attempts have been made to implement a passive or active robotic pointer as described in the referenced article, essentially, which consists of a pencil attached to an articulating arm, the arm having encoded joints which provide digital angular data. Such a robotic space pointer is a mechanically attached device and once calibrated can give the graphic representation of the pointer on a computer screen relative to the stereotactic data of the head.
One objective of the present invention is to provide a camera apparatus (optical) which can visualize a surgical field and digitize the view information from the camera and relate it via computer graphics means to image data which has been taken of the patient's anatomy by image scanning means (tomographic scanner). The relationship of the optical camera view and the image data will then make quantitative the anatomy seen in the camera view and also make quantitative the position of surgical instruments such as probes, microscopes, or space pointers to the anatomy via the registration of the camera view to the image data.
Another objective of the present invention is to make an optically coupled space pointer which accomplishes the same objectives as the robotic arm mechanically coupled space pointer, e.g., give ongoing positional correspondence between a position in a patient's brain and the tomographic image (see Kosugi et al). The optical coupling would free the surgeon from any sterility questions, provide an obstruction-free device, and avoid the encumbrances of a bulky mechanically coupled instrument.